Vehicles are generally equipped with audio devices that play an audio sound in a cabin. JP2776092B and JP1993-085288A disclose audio devices that perform localization of an audio sound so that a person(s) on board is able to hear the audio sound from a given position in a cabin.
Meanwhile, vehicles which are focused on the enjoyment of traveling, such as sports cars, are required to actively cause a person(s) on board, especially a vehicle driver, to hear (listen to) an engine sound. That is, since the engine sound is a good indication of a vehicle state, it becomes an extremely important element in the enjoyment of traveling. Therefore, when the audio device is operating, how to effectively cause the person(s) on board to hear the engine sound while also hearing the audio sound is important.